Conventionally, for vehicular lighting apparatuses, there has been known a technique of automatically shifting the beam state of a headlight according to the environmental conditions of the vehicle.
For example, in Patent Document 1, there is disclosed a vehicular lighting apparatus which sets the beam state of a headlight to a low-beam state during normal running of the vehicle, and shifts the beam state of the headlight from the low-beam state to a high-beam state when the vehicle-to-vehicle distance between the subject vehicle and a preceding vehicle running ahead of the subject vehicle becomes greater than or equal to a predetermined distance and the vehicle speed of the subject vehicle becomes greater than or equal to a predetermined vehicle speed.
Moreover, in recent years, there has been proposed a technique of running while keeping a predetermined vehicle-to-vehicle distance by adjusting the vehicle speed in accordance with a forward vehicle.
For example, in Patent Document 2, there is disclosed an auto-cruise apparatus which performs, in response to a predetermined manipulation of an inputting unit by the vehicle driver, automatic following by controlling the vehicle speed, with its upper limit set to a predetermined vehicle speed, so as to keep the vehicle-to-vehicle distance between a forward vehicle and the subject vehicle at a predetermined vehicle-to-vehicle distance.
Moreover, to improve the visibility of a vehicle by the surroundings, there has been provided a technique of DRL (Daytime Running Lamps), according to which the vehicle runs in daytime with the headlights of the vehicle turned on.
For example, in Patent Document 3, there is disclosed a vehicular lighting apparatus which sets a second lighting device to a daytime-on state based on both an on state of a headlight, which is capable of illuminating the advancing direction of the vehicle, and the operational position of an ignition switch of the vehicle.    PATENT DOCUMENT 1 Japanese Patent Application Publication No. JPS62253544A    PATENT DOCUMENT 2 Japanese Patent Application Publication No. JP 2002178786A    PATENT DOCUMENT 3 Japanese Patent Application Publication No. JP2005199794 A
However, with the above technique described in Patent Documents 1 and 2, though the beam state of the headlight is set to the low-beam state during normal running of the vehicle, there is still a possibility that the headlight dazzles occupants of forward vehicles, which include oncoming vehicles and preceding vehicles, when the vehicle is following a preceding vehicle or the vehicle-to-vehicle distance between the vehicle and a preceding vehicle is short.
Moreover, with the above technique described in Patent Documents 2 and 3, daytime running lighting is performed for improving the visibility of a vehicle by the surroundings in daytime. However, when the vehicle is following a preceding vehicle or the vehicle-to-vehicle distance between the vehicle and a preceding vehicle is short, it is easy for the visibility of the vehicle by the surroundings to be improved due to the presence of the preceding vehicle. Consequently, the daytime running lighting may become unnecessary.
However, in such a vehicle where daytime running lighting is available, the daytime running lamps are turned on at the same time as start of the engine, and in many cases the daytime running lamps cannot be turned off during operation. Consequently, electric power is continuously supplied from a battery even when the daytime running lighting is unnecessary, causing a problem of excessively consuming the battery power.
The present invention has been made in view of the above-described problems and aims to provide a vehicular lighting apparatus which can lower the degree of dazzling an occupant of a forward vehicle and the battery load of the subject vehicle.